[Bridge] question about bridge code

[lkcd]

br_nf_forward_ip() {
    parent = bridge_parent(out);
    NF_HOOK(pf, NF_INET_FORWARD, skb, brnf_get_logical_dev(skb, in), parent, 
br_nf_forward_finish);
}
 
here, i suppose pf = NFPROTO_IPV4,    i think  the return of 
brnf_get_logical_dev(skb, in) equals parent ?
 
then when calls iptable_filter_hook to match iptables rules , how to distinct 
in and out devices?
 
thanks